Many different types of equipment may have a headset connected thereto. The equipment includes mobile phones, pdas, mp3 players etc. The headset connection is generally made by way of a jack which plugs into the equipment or may be by an equivalent wireless connectivity.
In the case where the headset is also equipped with a microphone, the headset includes a send/end button which allows the user to start and finish a voice transmission for example for a phone call. The button press is detectable in the device, using a serial button circuit as shown in FIG. 1. The button 100 located in the headphone is serially connected and is normally closed. When the headset is inserted or removed or the button is pressed the circuit in for example FIGS. 2a and 2b detected these events.
For FIG. 2a when the headset is inserted the MCB voltage is driven to zero by the low impedance of the microphone and the flag rises to 1. With reference to FIG. 2b, when the send/end button is pressed the current flow through the switch is cut and the MCB voltage, rises to 2.775V. This causes the flag to drop to 0. The flag events are an indicator of the state of the headset and are used to start and finish a phone call. The detection system for the switch as shown is in essence a low value DC pull-up current source and a voltage comparator having a threshold set midway between ground and an audio supply. This mode of operation is highly efficient and allows a long standby period with minimum power consumption.
A need has now arisen to have a different mode of operation of a headset. That is to have voice activated dialing or control using the headset, for example for switching the phone from standby to active mode or vice-versa. In these situations there are more states than in the prior art mode of operation and thus detection of these is more complex. In addition, the standby power consumption modes must be preserved in order that the different operational modes do not impact battery functionality and that all the different states of the microphone can be identified without unnecessary power consumption. A further consideration which is taken into account is to adopt more cost effective means of switching on the headset, for example to use a parallel rather than serial switch.
An object of the present invention is to overcome at least some of the problems associated with the prior art. Another object of the present invention is to provide a low power detection system for recognising different states of a headset fitted with a parallel and/or series switch.